Currently, wireless communication systems such as a mobile phone system and a wireless local area network (LAN) are widely used. In addition, in the field of wireless communication, in order to further improve a communication speed and a communication capacity, a next-generation communication technology is continuously discussed. In, for example, 3rd Generation Partnership Project (3GPP) serving as a standardization body, standardization of a communication standard called Long Term Evolution (LTE) and standardization of a communication standard called LTE-Advanced (LTE-A) based on LTE are completed or studied.
As one of such technologies regarding wireless communication, there is coordinated multi-point transmission and reception (hereinafter, called “coordinated communication” or “COMP” in some cases). The coordinated communication is, for example, a technology in which base stations perform, in a coordinated manner, wireless communication with one mobile station. Compared with a case of performing no coordinated communication, by performing coordinated communication with a mobile station located in an area in which the cell range (or a “service provision range”) of a base station and the cell range of another base station overlap with each other, it is possible to achieve the improvement of a throughput in the relevant mobile station and to achieve the enhancement of communication performance.
As technologies regarding such coordinated communication, there are, for example, the following technologies. In other words, for all users, a coordination scheduler calculates all proportional fairness (PF) metrics of coordination stop patterns. In addition, the coordination scheduler calculates, for each of sectors, a user whose PF metric is maximized in each of coordination patterns, and the coordination scheduler selects a coordination pattern in which the sum of the PF metrics of the relevant user is maximized. Note that the PF metric is, for example, a ratio of an instantaneous throughput to an average throughput.
In addition, there is a technology for defining inter-base station coordinated communication as effective if a throughput in a case of performing coordinated communication is higher than the total value of throughputs for respective base stations in a case of not performing the coordinated communication.
Furthermore, there is a technology for setting the allocation frequency of resources of a user terminal that performs a multi-site connection to 1/(the number of cooperative base stations of the multi-site connection) with respect to the allocation frequency of resources of a user terminal that performs a single-site connection.
According to this technology, it is thought that it is possible to enhance the throughput of a user terminal located in a cell boundary and to suppress the reduction of a total throughput of a cellular mobile communication system.
Furthermore, there is a technology for switching, based on a communication speed requested by a terminal, between communication modes (for example, a mode in which only one base station and one terminal perform communication and a mode in which simultaneous communication with terminals is performed while a base station control station causes base station to cooperate with one another).
According to this technology, it is thought that it is possible to reduce a feedback amount while satisfying the communication speed requested by the terminal.
Furthermore, there is a technology in which the sum or product of actual measured values of throughputs of respective base station devices is compared with a default value in a centralized control station and based on the comparison result thereof, a communication parameter such as the number of terminals subordinated to a base station device is determined.
According to this technology, it is thought that it is possible to enhance the efficiency of wireless communication in a wireless communication system in which an interference source exists in the neighborhood thereof, thereby generating an interference signal.
Furthermore, there is a technology in which if the aggregate throughput of a coordinated transmission group in a case of adding a selection target cell and a selection target user is higher than the sum of the throughputs of the coordinated transmission group and the selection target cell in a case of not adding the selection target cell, the relevant cell and the relevant user are added to the coordinated transmission group.
According to this technology, it is thought that it is possible to dynamically determine a cell and a user, which are to be added to the coordinated transmission, and to provide a multi-cell coordination method capable of maximizing the throughput of a super cell.
As nonpatent literatures, there are Ogata, Daigo, et al., “A Study on Multi-BS Cooperative Transmission Control in the Cellular Mobile Communication”, Technical report of IEICE. RCS, RCS2011-16 (2011-4) and Nagate, Atsushi, et al., “[Tutorial Lecture] Basic Field Experiment of Multi-BS Cooperative Transmission Control”, Technical report of IEICE. RCS, RCS2011-170, SR2011-74, AN2011-48, USN2011-50 (2011-10).
As patent literatures, there are Japanese Laid-open Patent Publication No. 2011-142375, Japanese Laid-open Patent Publication No. 2013-93879, Japanese Laid-open Patent Publication No. 2014-17800, and Japanese Laid-open Patent Publication No. 2010-246114.